This invention relates to hydraulic hoists. In particular, this invention relates to a telescopic hydraulic hoist having a plurality of telescoping tube stages.
Telescopic hydraulic hoists are used in many applications. One popular use for telescopic hydraulic hoists is in heavy trucks, for example dump trucks, which require a strong, rigid lifting mechanism to raise the truck""s container or bed for dumping heavy materials such as rubble, dirt, gravel etc.
U.S. Pat. No. 5,983,778 issued Nov. 16, 1999 to Dawson, entitled xe2x80x9cTelescopic Hydraulic Hoist Apparatus,xe2x80x9d which is incorporated herein by reference, discloses a telescopic hydraulic hoist formed from a non-corrosive material such as aluminum. The hoist is provided with bearings and hydraulic seals about the bottom portion of each moving stage of the hoist. The bearings and seals are maintained within the hoist, and are thus not exposed to dust or particulate matter from outside the hoist. Air flows into and out of the air spaces between adjacent stages of the hoist through air breathers which are provided in gland nut bearings threadedly engaged to the exposed end of each tube stage.
The hoist disclosed in U.S. Pat. No. 5,983,778 may also include variable length stroke limiters, which limit the extension of the tube stages to varying degrees, and a cushion member which partially closes off the hydraulic inlet as the innermost stage is fully retracted to slow the hoist motion in the final stages of retraction. However, as is typical in telescopic hoist designs, the retracting movement of the various tube stages in the telescopic hoist is limited by the use of a stop ring inserted near the bottom of the inside diameter of each tube stage, which prevents further retraction of each moving stage once it has reached its fully collapsed position.
The stop ring may comprise a washer welded to the interior wall or a machined annular insert which is fitted into a groove circumscribing the interior wall of the tube stage. This presents a point of potential weakness in the hoist design, since in the former case the quality of the weld will affect the performance and durability of the tube stage, and in the latter case the groove creates a weak point around the tube wall. Also, the ring can become dislodged from the stage or otherwise distorted, causing a tube stage to fall through the next broader tube stage when the hoist is retracting and resulting in damage to the hoist.
Furthermore, the differential diameters of the tube stages affects the rigidity or stability of the hoist in the extended position. Given a constant wall thickness, as the diameter of each tube stage decreases, the length of the tube stage which can safely extend beyond the next broader tube stage also decreases. Increasing the wall thickness of the tube stages would enhance the stability of the hoist, but is not a desirable solution because it also increases the weight of the hoist.
One way to increase the stability of the hoist structure is to increase the overlap between adjacent tube stages of the hoist when the hoist is in its fully extended position. The greater the overlap between one telescopic stage and the next, the more rigid and stable is the structure of the extended hoist. However, increasing the overlap between adjacent tube stages correspondingly decreases the usable length of each tube stage and commensurately limits the maximum extension length of the hoist.
The present invention overcomes these disadvantages by providing a telescopic hydraulic hoist which improves stability and rigidity in the extended position without sacrificing the maximum extension length of the hoist. A hoist according to the invention improves stability by providing greater overlap between tube stages. The invention further eliminates the need for a stop ring, and thus provides a telescopic hydraulic hoist with fewer machined parts which may be dislodged or damaged in operation to thereby extend the life of the hoist, simplify assembly of the hoist, reduce the cost of the hoist components, and eliminate the weak point resulting from the inclusion of a groove or weld used to retain the stop ring in place in a conventional hoist by allowing the wall of the tube stage to be formed to a uniform thickness.
The invention accomplishes this by providing a base member having a recess into which intermediate and inner tube stages recede when the hoist is in a fully collapsed position. The invention also accomplishes this by providing a stop-collar on the gland nut bearings which defines a limit of retraction for each intermediate tube stage, the collar extending beyond an inner limit of the next broader tube stage so that a tube stage when fully retracted thus contacts the next broader tube stage, dispensing with the need for additional components such as stop rings.
The present invention thus provides a telescopic multi-stage hydraulic hoist, comprising a hydraulic fluid inlet in communication with an interior of the hoist, an inner tube stage having a contained end and an exposed end, at least one intermediate tube stage having a contained end and an open exposed end and comprising an intermediate gland nut bearing affixed to the exposed end of the at least one intermediate tube stage, the inner tube stage being disposed in the at least one intermediate tube stage in telescoping relation and being extendible through the open end of the at least one intermediate tube stage to an extended position and retractable through the open end of the at least one intermediate tube stage to a collapsed position, an outer tube stage having a first end and a second open end and comprising an outer gland nut bearing affixed to the open end of the outer tube stage and a base member affixed to the first end of the outer tube stage in sealed relation, the at least one intermediate tube stage being spaced from the outer tube stage by the outer gland nut bearing and being extendible through the open end of the outer tube stage to an extended position and retractable through the open end of the outer tube stage to a collapsed position, wherein the exposed end of at least the inner tube stage comprises a stop-collar which overlaps an exposed end of the at least one intermediate tube stage such that the stop-collar contacts the exposed end of the at least one intermediate tube stage when the inner tube stage is in a fully collapsed position.
The present invention further provides a telescopic multi-stage hydraulic hoist, comprising a hydraulic fluid inlet in communication with an interior of the hoist, an inner tube stage having a contained end and an exposed end, at least one intermediate tube stage having a contained end and an open exposed end and comprising an intermediate gland nut bearing affixed to the exposed end of the at least one intermediate tube stage, the at least one intermediate tube stage being disposed in a next broader tube stage in telescoping relation and being extendible through the open end of the next broader tube stage to an extended position and retractable through the open end of the next broader tube stage to a collapsed position, the inner tube stage being disposed in the at least one intermediate tube stage in telescoping relation and being extendible through the open end of the at least one intermediate tube stage to an extended position and retractable through the open end of the at least one intermediate tube stage to a collapsed position, an outer tube stage having a first end and a second open end and comprising an outer gland nut bearing affixed to the open end of the outer tube stage and a base member affixed to the first end of the outer tube stage in sealed relation, the at least one intermediate tube stage being spaced from the outer tube stage by the outer gland nut bearing and being extendible through the open end of the outer tube stage to an extended position and retractable through the open end of the outer tube stage to a collapsed position, the exposed end of at least the inner tube stage comprises a stop-collar which overlaps the exposed end of the next broader tube stage, wherein when the inner tube stage reaches a fully collapsed position the stop-collar of the inner tube stage contacts the exposed end of the next broader tube stage.
The present invention further provides a telescopic multi-stage hydraulic hoist, comprising a hydraulic fluid inlet in communication with an interior of the hoist, an outer tube stage having a first end and a second open end and comprising an outer gland nut bearing affixed to the open end of the outer tube stage, at least one intermediate tube stage disposed within the outer tube stage in telescoping relation, the at least one intermediate tube stage having a contained end and an exposed end and comprising an intermediate gland nut bearing affixed to the open end, the intermediate tube stage being extendible through the open end of a next broader intermediate tube stage or the outer tube stage to an extended position and retractable through the open end of the next broader intermediate tube stage or the outer tube stage to a collapsed position, an inner tube stage disposed within the at least one intermediate tube stage in telescoping relation, the inner tube stage having a contained end and an exposed end and being extendible through the open end of the at least one intermediate tube stage to an extended position and retractable through the open end of the at least one intermediate tube stage to a collapsed position, a base member affixed to the first end of the outer tube stage in sealed relation, the base member comprising a recess, and a stop structure for arresting the retraction of the inner tube stage, whereby the contained end of at least the inner tube stage recedes into the recess in the base member when the hoist is in a fully collapsed position.
In further aspects of the hoist of the invention: the stop-collars project from the gland nut bearings; each stop-collar contacts the gland nut bearing of the next broader tube stage; the gland nut bearings each comprise a wiper and a portion of the stop-collar of one tube stage which contacts the gland nut bearing of the next broader tube stage is provided with an annular recess into which the wiper of the next broader tube stage projects when the one tube stage is in the fully collapsed position; the base member comprises a recess, wherein the contained end of the inner tube stage recedes into the recess in the base member when the hoist is in a fully collapsed position; the hoist comprises a plurality of intermediate tube stages, wherein at least one intermediate tube stage recedes into the recess in the base member when the hoist is in a fully collapsed position; the base member is threadedly engaged to the outer tube stage; the base member comprises a neck bearing threads for engagement to the outer tube stage; and/or at least one of the intermediate tube stages abuts the neck of the base member when in the fully collapsed condition.
The present invention further provides a telescopic multi-stage hydraulic hoist, comprising a hydraulic fluid inlet in communication with an interior of the hoist, an outer tube stage having a first end and a second open end and comprising an outer gland nut bearing affixed to the open end of the outer tube stage, an inner tube stage disposed within the outer tube stage in telescoping relation, the inner tube stage having a contained end and an exposed end and being extendible through the open end of the outer tube stage to an extended position and retractable through the open end of the outer tube stage to a collapsed position, and a base member affixed to the first end of the outer tube stage in sealed relation, comprising a neck bearing threads for engagement to the outer tube stage, whereby the contained end of the inner tube stage abuts the neck of the base member when the hoist is in the fully collapsed condition.